Also adding to the frustration is the conflicting reports from the Korean government and the coast guard as to what caused the ferry to sink.

The coast guard says it investigating why the ship did not travel the recommended route to Jeju Island and whether the crew inspected the ship's safety equipment before departing.

The ship's captain, 69-year-old Lee Jun Seok, is being questioned on why he changed the ship's path to an area known to have rocky shoals and shallow reefs.

But the the South Korean Ministry of Oceans and Fisheries says the passenger ship did not sink in an area with rocky shoals or shallow reefs.

Analysis from Matthew Carney

There are all types of stories, reports coming out about the captain that the coastguard is investigating - that he did veer off the established route and veered into an area where there's rocky shoals and shallow reefs.

He's being investigated by the coastguard now. And that's where we're at.

The government subsequently - there seems to be some kind of fight here between the coastguard and the government - has come out and said "We're doing our own investigation. And, in fact, the ship didn't hit rock or a reef."

The tidal areas are very steep in that area - some of the biggest tidal movements are in that area. So depending, on the time of day you'll see the hull and then you won't.

But this is what puzzles me - the government is saying that the ship sank in 30 metres of water, but here we can see it, for everyone to see.

The ministry has sent its own investigators to the country's south-western coast.

It says the ship is unlikely to have hit rocks given the water where it sunk is 30 metres deep and just six metres of the ferry's hull is submerged while travelling.

Voice recordings have also emerged revealing that passengers on board the ferry were ordered not to move as it began to turn over.

Audio recordings from the sinking ship's loudspeaker system obtained by South Korean media warned "Don't move. If you move, it's dangerous."

Many survivors say they faced a terrifying choice - obey the commands or put on a life jacket and jump into the cold ocean.

One survivor said "The kids were forced to stay put, so only the ones that moved survived".

Relatives gather in anxious wait for news

The gymnasium where hundreds spent the night on the floor looked like a refugee camp or triage station, with some overwrought relatives being treated with saline drips after collapsing with exhaustion.

One father wept silently, covering his face with his hands as his wife tried to console him.

Some like Park Yu-Shin, whose student daughter is missing, had been able to stay in contact with their loved ones until the last moment.

"She was telling me: 'We're putting on our life vests. They're telling us to wait and stay put, so we're waiting, mum. I can see a helicopter'," Ms Park recalled, her voice breaking with emotion.

Unable to sleep, some relatives spent the night on the quay of Jindo harbour, staring out to sea as if willing their children back to safety.

"My daughter is out there, somewhere out there in the cold sea," said one anguished mother.

Every time one of the many coast guard vessels involved in the search returned to the harbour, there was a flurry of activity as relatives jostled on the quayside, hoping for some fresh news.

Urging the rescue teams not to give up, some said they had received recent text messages from their children trapped in the boat.

But their claims could not be verified and there was no official confirmation of any contact with trapped survivors after the boat sank.

Amid the anxiety and grief there was also a growing sense of anger and frustration.

One mother blocked Mr Chung's path as he tried to leave, saying: "Don't run away, Mr Prime Minister. Please tell us what you're planning to do."

Han Young-Hee, whose sister was on the ferry with her husband, showed AFP the pictures the couple had texted her before the accident.

"This is her posing on the deck with a coffee. They were very excited about their trip," Ms Han said.

"That was early in the morning. There was nothing afterwards. Nothing," she said.

In the gymnasium, volunteers did what they could to comfort the relatives, handing out blankets, instant noodles and coffee, while medical staff tended to those in physical distress.

Small plastic tents were set up at the quay for those who preferred to wait outside.

The desperation for fresh news was tempered only by the fear that it would be the worst news, as was the case when a coast guard official picked up the microphone to announce a sixth body had been recovered.

Then he named the victim and one set of parents' hopes were shattered forever.